Camshaft phasers for varying the timing of combustion valves in internal combustion engines are well known. A first element, known generally as a sprocket element, is driven by a chain, belt, or gearing from an engine's crankshaft. A second element, known generally as a camshaft plate, is mounted to the end of an engine's camshaft. A common type of camshaft phaser used by motor vehicle manufactures is known as a vane-type camshaft phaser. U.S. Pat. No. 7,421,989 shows a typical vane-type camshaft phaser which generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is supplied via a multiport oil control valve, in accordance with an engine control module, to either the advance or retard chambers, to change the phase relationship of the rotor relative to the stator, as required to meet current or anticipated engine operating conditions. In order to selectively prevent a change of angular position of the rotor relative to the stator at a predetermined location, a lock pin is provided in one of the vanes which selectively engages a lock pin seat provided in an element fixed to the stator. Preventing a change of angular position of the rotor relative to the stator using the lock pin may be desired, for example, when the internal combustion is being shut down or started up and pressurized oil is not sufficiently available to maintain a desired angular position of the rotor relative to the stator.
While vane-type camshaft phasers are effective and relatively inexpensive, they do suffer from drawbacks. First, at low engine speeds, oil pressure tends to be low, and sometimes unacceptable. Therefore, the response of a vane-type camshaft phaser may be slow at low engine speeds. Second, at low environmental temperatures, and especially at engine start-up, engine oil displays a relatively high viscosity and is more difficult to pump, therefore making it more difficult to quickly supply engine oil to the vane-type camshaft phaser. Third, using engine oil to drive the vane-type camshaft phaser is parasitic on the engine oil system and can lead to requirement of a larger oil pump. Fourth, for fast actuation, a larger engine oil pump may be necessary, resulting in additional fuel consumption by the engine. Lastly, the total amount of phase authority provided by vane-type camshaft phasers is limited by the amount of space between adjacent vanes and lobes. A greater amount of phase authority may be desired than is capable of being provided between adjacent vanes and lobes. For at least these reasons, the automotive industry is developing electrically driven camshaft phasers.
One type of electrically driven camshaft phaser being developed is shown in U.S. patent application Ser. No. 12/536,575; U.S. patent application Ser. No. 12/844,918; U.S. patent application Ser. No. 12/825,806; U.S. patent application Ser. No. 12/848,599; U.S. patent application Ser. No. 12/965,057; U.S. patent application Ser. No. 13/102,138; U.S. patent application Ser. No. 13/112,199; and U.S. patent application Ser. No. 13/155,685; which are commonly owned by Applicant and incorporated herein by reference in their entirety. The electrically driven camshaft phaser is an electric variable camshaft phaser (eVCP) which comprises a flat harmonic drive unit having a circular spline and a dynamic spline linked by a common flexspline within the circular and dynamic splines, and a single wave generator disposed within the flexspline. The circular spline is connectable to either of an engine camshaft or an engine crankshaft driven rotationally and fixed to a housing, the dynamic spline being connectable to the other thereof. The wave generator is driven selectively by an electric motor to cause the dynamic spline to rotate past the circular spline, thereby changing the phase relationship between the crankshaft and the camshaft. Unlike vane-type camshaft phasers which rely on pressurized oil to change the angular position of the rotor relative to the stator and therefore the phase relationship of the crankshaft relative to the camshaft, the eVCP uses the electric motor to change and hold the phase relationship of the crankshaft relative to the camshaft when the internal combustion engine is running, shutting down, and restarting. However, a variation in the phase relationship of the crankshaft to the camshaft may occur until the system relearns the phase relationship of the crankshaft relative to the camshaft when the internal combustion engine is restarting. Consequently, it may be desirable to have a means for positively preventing a change in phase relationship of the eVCP, thereby guaranteeing a known phase relationship of the crankshaft relative to camshaft and eliminating the need to relearn the phase relationship of the crankshaft relative to the camshaft.
What is needed is an eVCP with means for preventing a change in phase relationship between the crankshaft and the camshaft; more particularly, what is needed is an eVCP with a lock pin for preventing rotation of an input member of the eVCP relative to an output member of the eVCP.